1. Field of the Invention
The present invention relates to a semiconductor device, and particularly to a semiconductor device capable of efficiently releasing the heat generated in operation.
2. Description of the Background Art
In recent years, there has been an increasing demand for rapid operation of integrated circuits (ICs) to process mass information. Accordingly, the number of signal pins provided in ICs is also increased for inputting and outputting predetermined signals. Furthermore, increasing electricity consumption of ICs results in increasing the number of power supply pins for supplying power.
Also, there has been a demand for a package sealing a semiconductor chip that is closer in size to the semiconductor chip so as to achieve mounting at high density.
As a first prior art, as an exemplary semiconductor device including a package which seals a semiconductor chip will now be described with reference to the drawings. FIG. 7 shows the structure of a fine-pitch ball grid array (referred to as "a fine-pitch BGA" hereinafter). Referring to FIG. 7, a semiconductor chip 102 is die-bonded on one surface of a glass sheet (referred to as a "tape" hereinafter) 106 impregnated with epoxy resin with an adhesion layer interposed therebetween. Formed near a periphery of tape 106 are a plurality of pad electrodes 107, each electrically connected to a predetermined region of semiconductor chip 102 via a gold wire 104.
Formed on another surface of tape 106 are a plurality of solder balls 108 each electrically connected to pad electrode 107 via a predetermined wiring formed at tape 106. Semiconductor chip 102 is sealed on tape 106 by molded resin 110.
Fine-pitch BGA, allowing solder balls as electrode pins to be arranged in an array, is advantageous in forming more pins in a small package.
An another exemplary semiconductor device as a second prior art will now be described with reference to the drawings. FIG. 8 shows the configuration of a chip-scale package (referred to as a CSP hereinafter). Referring to FIG. 8, provided at a surface of semiconductor chip 102 are a plurality of external electrodes 109 each electrically connected to a predetermined region of semiconductor chip 102 via a metal wiring 111 and a pad electrode 107. Semiconductor chip 102 is sealed by molded resin 110.
The CSP, having approximately the same size as semiconductor chip 102, allows more pins to be formed. The CSP also allows mounting at high density since a relatively small area is required for mounting it on a substrate.
In the fine-pitch BGA and CSP described above, however, a relatively large amount of electricity is consumed and the semiconductor chip disadvantageously generates heat. Accordingly, various approaches have been taken for releasing such heat.
As a third prior art, an exemplary semiconductor device effectively releasing such heat will now be described based on a semiconductor device disclosed in Japanese Patent Laying-Open No. 7-50368. FIG. 9 is a cross section of the semiconductor device disclosed in Japanese Patent Laying-Open No. 7-50368. FIG. 10 is a plan view of the semiconductor device excluding a cap. Referring to FIG. 9, semiconductor chip 120 has a back surface fixed to a package 125 and is sealed in a space formed by a cap 123 and package 125. A gap is formed between an upper surface of semiconductor chip 120 and an inner surface of cap 123.
A power supply on semiconductor chip 120 is supplied from an external circuit via a pin 129, a wiring 127, an electrode for power supply 124, solder 132 and a pad for power supply 122. Signals between the external circuit and semiconductor chip 120 are communicated via a pin 130, a wiring 128, a lead 126, a bonding wire 131 and a bonding pad 121. Pad for power supply 122, formed at a surface of semiconductor chip 120, can be increased in area, as shown in FIG. 10.
In operation, the semiconductor device allows the heat generated at semiconductor chip 120 to be transferred to package 125 via the back surface of semiconductor chip 120 and also to cap 123 via pad for power supply 122, solder 132 and electrode for power supply 124. Thus, both package 125 and cap 123 can release heat, and the heat generated at semiconductor chip 120 can be sufficiently released to the environment.
Furthermore, the provision of electrode for power supply 124 and pad for power supply 122 allows reduction of the power supply to semiconductor chip 120 via bonding pad 121. Accordingly, bonding pad 121 can be used for signal communication between semiconductor chip 120 and the external circuit by the reduction. Thus, more bonding pads 121 can be used for signal communication than conventional.
However, the semiconductor device of the third prior art example described above has the disadvantages described below. Firstly, since the power for semiconductor chip 120 is supplied via electrode for power supply 124, semiconductor chip 120 does not require a bonding pad for power supply and can thus be provided with more bonding pads for signal communication instead. However, since the power is supplied to semiconductor chip 102 via pin 129 provided at package 125, the total number of pins 129 provided at a predetermined region of package 125 does not vary, which makes it difficult to provide any additional pin for signal communication in that region.
Secondly, while the heat transferred to cap 123 is more effectively released to the external when cap 123 and package 125 have larger surface area, it can fail to be sufficiently released with relatively small cap 123 and package 125.